JP3595740B2

JP3595740B2 - Wireless communication system

Info

Publication number: JP3595740B2
Application number: JP25934699A
Authority: JP
Inventors: 岡秀浩松; 戸一郎瀬; 上康村
Original assignee: Toshiba Corp
Current assignee: Toshiba Corp
Priority date: 1999-09-13
Filing date: 1999-09-13
Publication date: 2004-12-02
Anticipated expiration: 2019-09-13
Also published as: JP2001086057A

Description

【０００１】
【発明の属する技術分野】
本発明は、移動体と無線通信を行うためのアレーアンテナを有する無線基地局と、無線基地局の制御を行う制御局との間で、光ファイバ等の有線通信媒体を介してデータ通信を行う無線通信システムに関する。
【０００２】
【従来の技術】
比較的カバーエリアの狭い複数の無線基地局と一つの集中制御局とを光ファイバで接続し、各基地局と制御局の間で無線信号を光信号に変換して伝送するＲＯＦ（ＲａｄｉｏＯｎＦｉｂｅｒ）システムは、信頼性および広帯域性の面で優れ、また、緻密なサービスを行うことができるため、ＦＴＴＨ（ＦｉｂｅｒＴｏＴｈｅＨｏｍｅ）や加入者系無線や、ＩＴＳ（ＩｎｔｅｌｌｉｇｅｎｔＴｒａｎｓｐｏｒｔＳｙｓｔｅｍ）用のインフラとして有効である。
【０００３】
特に、ＲＯＦシステムを構築する場合に、制御局に変復調器や制御装置を設けて、各基地局を必要最小限の装置構成とすれば、基地局の簡素化、小型化および低コスト化が可能になる。このため、多数の基地局を道路沿い、地下街、トンネル等に配置することができ、効率的でかつ経済的なインフラ構築が可能となる。
【０００４】
一方、基地局のアンテナとして、所望の端末局に対して指向性を持たせたり、あるいは他局からの干渉を抑圧したりして、任意の形状のカバーエリアを形成するアダプティブアンテナ技術が注目されている。
【０００５】
アダプティブアンテナ技術は、複数のアンテナ素子から送受信される信号に位相および振幅に関する重み付けを行って放射パターンを制御するものである。放射パターンの制御方式として、主に、増幅器や移相器などのアナログ素子による重み付けを行う手法と、ディジタル信号に変換した後にディジタル信号処理により複素重み付けを行う手法がある。
【０００６】
このアダプティブアンテナを基地局に備え、ＲＯＦ技術を用いて制御局と接続する無線通信システムがいくつか報告されている（例えば、特開平５−１０２８９４や特開平１０−１４５２８６）。アダプティブアンテナを有する無線通信システムでは、アンテナ素子ごとに異なる無線信号を、基地局と制御局間で相対位相差と相対強度差を維持したまま伝送する技術が必要となる。
【０００７】
このため、従来の報告では、ＲＯＦの伝送形態として、無線信号に周波数変換以外の信号処理を施さない波長多重伝送、あるいは、各ブランチにそれぞれ光ファイバを割り当てる手法が取られている。以下では、一つのアンテナ素子から送受信される信号を処理する系のことをブランチと呼ぶことにする。
【０００８】
各ブランチごとに光ファイバを設ける手法では、基地局と制御局を接続する光ファイバの本数が大幅に増加するため、光ファイバの利用効率が低くなるとともに、複数の基地局と接続される制御局側の光伝送系の構成が複雑化し、規模も大きくなる。すなわち、アダプティブアンテナを有する無線通信システムに対するＲＯＦ技術は、光伝送系部分の構成要素が複雑かつ大規模になるという問題があり、基地局及び制御局の構成を簡易・小型化するのが難しい。
【０００９】
これに対して、光ファイバによる伝送系において、一つの光源によって複数の無線信号を周波数軸で多重化する方式として、サブキャリア多重伝送（ＳＣＭ）が知られている。ＲＯＦの実現方法として、ＳＣＭを用いると、必要な光ファイバが送受信あわせて一本ですむため、システム構築が低コスト化でき、また、光合波器・光分波器が不要でかつ光源が一つですむ等のメリットがある。それゆえ、各ブランチの送受信信号を一旦周波数変換し、それぞれにサブキャリアを割り当てて光ファイバ内を伝送する方式が有効である。
【００１０】
【発明が解決しようとする課題】
しかしながら、上記の二つの手法では、各アンテナ素子にＥ／Ｏ変換器（電気／光変換器）とＯ／Ｅ変換器（光／電気変換器）の対を割り当てるため、基地局及び制御局には、ブランチ数分の対が必要となる。つまり、基地局及び制御局の光伝送部の構成要素が大幅に増加し、構成が複雑化して大きくなるという問題がある。
【００１１】
また、基地局と制御局間で波長多重伝送を行う場合には、光合波器、光分波器、および光源の波長制御器等の構成を追加する必要があり、非常に高価なシステムになってしまう。
【００１２】
また、ＳＣＭを用いる方式では、基地局−制御局間でキャリア同期とタイミング同期をとらなければ、多重化された各ブランチの信号を正しく取り出すことができないという問題がある。
【００１３】
本発明は、このような点に鑑みてなされたものであり、その目的は、構成を複雑にすることなく、制御局から基地局に送信される送信信号の位相および振幅調整を簡易かつ精度よく行うことができる無線通信システムを提供することにある。
【００１４】
【課題を解決するための手段】
上述した課題を解決するために、請求項１の発明は、無線通信端末と、この無線通信端末と無線通信を行う基地局と、この基地局と有線伝送路を介して接続された制御局とからなる無線通信システムにおいて、前記基地局は、複数のアンテナ素子からなるアレーアンテナと、前記有線伝送路を介して前記制御局から伝送されてきた前記各アンテナ素子に対応した各々の送信信号を、前記有線伝送路を介して前記制御局にフィードバックするフィードバック手段を有し、前記制御局は、前記フィードバック手段からフィードバックされた前記各送信信号の中から、少なくとも二つの信号を比較し、位相差及び又は振幅変動量を検出する比較検出手段と、前記比較検出手段で検出した位相差及び又は振幅変動量に基づいて、前記複数のアンテナ素子に対応した各々の送信信号を補償する補償手段とを有する。
請求項１の発明では、制御局が基地局に伝送した送信信号と、そのフィードバック信号とを比較して、位相差および振幅変動量を検出するため、簡易な構成で精度よく位相および振幅調整を行うことができる。
【００１５】
請求項２および３の発明では、送信信号を制御局にフィードバックする際、フィードバック信号にパイロット信号を挿入するため、このフィードバック信号により、受信系での相対位相差と相対振幅変動量を検出することができ、その検出結果により、送信系の相対位相差と相対振幅変動量を検出することもできる。
【００１６】
請求項４の発明では、各送信信号の絶対位相差と絶対振幅変動量を検出することができる。
【００１７】
請求項５の発明では、各アンテナ素子に対応する送信信号のいずれかを任意に選択できるため、各送信信号の絶対位相差と絶対振幅変動量を検出することができる。
【００１８】
請求項５〜７の発明では、送信信号を制御局にフィードバックするための専用伝送媒体を設けるため、パイロット信号なしに、相対位相差と相対振幅変動量を検出することができる。
【００１９】
請求項８の発明では、位相差と振幅変動量を補償するための校正係数を加味した重み係数を演算するため、送信信号の重み付けと校正をまとめて行うことができる。
【００２０】
【発明の実施の形態】
以下、本発明を適用した無線通信システムについて、図面を参照しながら具体的に説明する。
【００２１】
（第１の実施形態）
図１は本発明に係る無線通信システムの第１の実施形態のブロック図である。図１のシステムは、アダプティブアンテナ１を有する基地局２と制御局３とを光ファイバ４で接続し、サブキャリア多重伝送を行う例を示している。図１のアダプティブアンテナ１は、３つのアンテナ素子１ａ〜１ｃを有するが、アンテナ素子１ａ〜１ｃの数には特に制限はない。
【００２２】
図１の基地局２は、受信系の構成として、送受信の切り替えを行うサーキュレータ５ａ〜５ｃと、送受信信号の合成を行う合成器（合成手段）６ａ〜６ｃと、制御局３にフィードバックする送信信号にパイロット信号を挿入するパイロット信号挿入器（パイロット信号挿入手段）７と、パイロット信号挿入器７の出力信号を増幅するローノイズアンプ８ａ〜８ｃと、ローノイズアンプ８ａ〜８ｃの各出力信号をそれぞれ異なる周波数信号にダウンコンバートする周波数変換器（第１の周波数変換手段）９ａ〜９ｃと、周波数変換器９ａ〜９ｃから出力された各周波数信号を多重化する合成器（周波数多重化手段）１０ａ〜１０ｃと、合成器１０ａ〜１０ｃで合成された信号を光信号に変換して光ファイバ４を介して制御局３に伝送する電気／光変換器（第１の電気／光変換手段）１１とを有する。
【００２３】
また、図１の基地局２は、送信系の構成として、制御局３から伝送されてきた光信号を電気信号に変換する光／電気変換器１２と、光／電気変換器１２の出力信号を複数の周波数信号に分配する分配器１３と、分配器１３で分配された各周波数信号を無線周波数の信号に変換する周波数変換器１４ａ〜１４ｃと、周波数変換器１４ａ〜１４ｃの出力信号を増幅する増幅器１５ａ〜１５ｃと、増幅器１５ａ〜１５ｃの出力信号をサーキュレータ５ａ〜５ｃと合成器６ａ〜６ｃに分岐させるカップラ１６ａ〜１６ｃとを有する。
【００２４】
この他、図１の基地局２は、周波数変換器９ａ〜９ｃ，１４ａ〜１４ｃにそれぞれ局部発振信号を供給する周波数シンセサイザ１７を有する。周波数シンセサイザ１７は、それぞれ周波数の異なる信号を出力する複数の局部発振器を有するか、あるいは、一つの局部発振器と、この局部発振器から出力された局部発振信号を逓倍または分周して複数の周波数信号を出力する分周器とを有する。
【００２５】
一方、図１の制御局３は、受信系の構成として、基地局２から伝送されてきた光信号を電気信号に変換する光／電気変換器（光／電気変換手段）２１と、光／電気変換器２１の出力信号を複数の信号に分配する分配器（分配手段）２２と、分配器２２から出力された各信号をそれぞれ異なる周波数の信号に変換する周波数変換器（第３の周波数変換手段）２３ａ〜２３ｃと、周波数変換器２３ａ〜２３ｃの出力信号に基づいて送信信号のフィードバック信号を検出するフィードバック信号検出器（フィードバック手段）２４と、フィードバック信号に基づいて校正係数を演算する校正係数演算回路（比較手段）２５と、校正係数に基づいて送受信用の重み係数を演算するアダプティブアンテナ重み係数演算回路（重み係数演算手段）２６と、演算された重み係数に基づいて受信信号の重み付けを行う乗算器（第１の重み付け手段）２７ａ〜２７ｃと、乗算器２７ａ〜２７ｃの各出力信号を合成する合成器２８と、合成器２８で合成された信号を復調する復調器２９とを有する。
【００２６】
また、図１の制御局３は、送信系の構成として、送信用の変調信号を生成する変調器３１と、変調信号を複数に分配する分配器３２ａ〜３２ｃと、分配された変調信号を重み係数に基づいて重み付けする乗算器（第２の重み付け手段）３３ａ〜３３ｃと、乗算器３３ａ〜３３ｃの出力信号をそれぞれ異なる周波数の信号に変換する周波数変換器３４ａ〜３４ｃと、周波数変換器３４ａ〜３４ｃの出力信号を多重化する合成器３５と、合成器３５で多重化された信号を光信号に変換して光ファイバ４を介して基地局２に伝送する電気／光変換器３６とを有する。
【００２７】
この他、図１の制御局３は、周波数変換器２３ａ〜２３ｃ，３４ａ〜３４ｃにそれぞれ局部発振信号を供給する周波数シンセサイザ３７を有する。周波数シンセサイザ３７は、それぞれ周波数の異なる信号を出力する複数の局部発振器を有するか、あるいは、一つの局部発振器と、この局部発振器から出力された局部発振信号を逓倍または分周して複数の周波数信号を出力する分周器とを有する。本実施形態では、基地局２内の周波数シンセサイザ１７と制御局３内の周波数シンセサイザ３７は、周波数とタイミングの同期が取れていると仮定する。
【００２８】
図１の基地局２において、合成器６ａ〜６ｃ、パイロット信号挿入器７、ローノイズアンプ８ａ〜８ｃ、周波数変換器９ａ〜９ｃ、合成器９および電気／光変換器１１がフィードバック手段に対応し、周波数変換器８ａ〜８ｃ，９ａ〜９ｃ、合成器１０、および電気／光変換器１１が伝送手段に対応する。また、図１の制御局２において、重み係数演算回路２６と乗算器２７ａ〜２７ｃ，３３ａ〜３３ｃとが補償手段に対応し、フィードバック信号検出器２４が第１および第２の検出手段に対応する。
【００２９】
図１の基地局２は、制御局３から基地局２に伝送された送信信号を、アレーアンテナ１から放射する前に、基地局２内の受信系を介して制御局３にフィードバックする。また、制御局３は、フィードバック信号のうち２つの信号を比較し、送信信号の相対位相差と相対振幅変動量を補償するための校正係数を生成する。
【００３０】
以下、図１の無線通信システムの動作を説明する。アンテナ素子１ａ〜１ｃで受信された信号と制御局３から基地局２に伝送されてきた送信信号とは、合成器６ａ〜６ｃで合成された後、パイロット信号挿入器７によりパイロット信号が挿入される。その後、ローノイズアンプ８ａ〜８ｃを介して周波数変換器９ａ〜９ｃに入力され、各アンテナ素子１ａ〜１ｃに対応する各ブランチごとにそれぞれ異なる周波数に変換される。このとき、光ファイバ４や光源の周波数特性等に応じた中間周波数に変換するのが望ましい。中間周波数に変換することにより、光伝送系の構成を簡略化することができる。周波数変換器９ａ〜９ｃの出力信号は、合成器１０にて周波数が多重化された後、電気／光変換器１１にて光信号に変換されて基地局２に伝送される。
【００３１】
図２は合成器１０で周波数多重化された信号の周波数スペクトル図である。図２に示すように、アレーアンテナ１での受信信号と、パイロット信号と、制御局３からの送信信号とが、それぞれ異なる周波数間隔で配置され、これらを一群としてサブキャリアｆ１〜ｆ３が割り当てられる。なお、周波数変換器９ａ〜９ｃの内部に設けられる不図示の帯域フィルタは、各サブキャリアの信号群を通過可能な帯域を持っている必要がある。
【００３２】
制御局３に伝送されてきた光信号は、制御局３内の電気／光変換器２１にて再び電気信号に変換された後、分配器２２にて複数のブランチ信号に分配される。これらブランチ信号は、周波数変換器２３ａ〜２３ｃにて同一の周波数信号に変換された後、フィードバック信号検出器２４と乗算器２７ａ〜２７ｃに入力される。
【００３３】
フィードバック信号検出器２４は、周波数変換器２３ａ〜２３ｃの各出力信号の中から、制御局３が送信した送信信号と、パイロット信号と、アダプティブアンテナ１で受信された受信信号とを抽出する。
【００３４】
校正係数演算回路２５は、フィードバック信号検出器２４で抽出された各ブランチの送信信号のうち、いずれか一つのブランチの送信信号を基準として、残りのブランチの送信信号との相対位相差と相対振幅偏差を検出し、検出結果に応じた校正係数を演算する。
【００３５】
重み係数演算回路２６は、周波数変換器２３ａ〜２３ｃの出力信号と、校正係数演算回路２５で演算された校正係数と、ビーム制御のために計算された送信／受信ウェイトとに基づいて、送信信号に対する重み係数と受信信号に対する重み係数を演算する。
【００３６】
乗算器２７ａ〜２７ｃは、周波数変換器２３ａ〜２３ｃの出力信号と重み係数演算回路２６で演算された重み係数とを乗算して受信信号の重み付けを行う。重み付けされた受信信号は、復調器２９に入力されて復調される。
【００３７】
一方、制御局３内の変調器３１で変調された送信信号は、乗算器３３ａ〜３３ｃにて、重み係数演算回路２６で演算された重み係数と乗算されて、重み付けされる。重み付けされた送信信号は、周波数変換器３４ａ〜３４ｃにてそれぞれ異なる周波数の信号に変換された後、合成器３５にて周波数多重化される。
【００３８】
周波数多重化された送信信号は、電気／光変換器３６にて光信号に変換された後、光ファイバ４を介して基地局２に伝送される。
【００３９】
基地局２に伝送されてきた光信号は、分配器１３にて複数のブランチ信号に分配され、各ブランチ信号は周波数変換器１４ａ〜１４ｃに入力されて無線周波数の信号にアップコンバートされる。
【００４０】
周波数変換器１４ａ〜１４ｃの各出力信号は、増幅器１５ａ〜１５ｃに入力されて増幅された後、カップラ１６ａ〜１６ｃとサーキュレータ５ａ〜５ｃを介してアンテナ素子１ａ〜１ｃに入力される。
【００４１】
次に、図１のフィードバック信号検出器２４、校正係数演算回路２５、および重み係数演算回路２６の詳細構成および動作について説明する。
【００４２】
校正係数演算回路２５は、図３に詳細構成を示すように、位相差検出器５１と、振幅比検出器５２と、演算器５３とを有する。位相差検出器５１と振幅比検出器５２の双方には、周波数変換器２３ａ〜２３ｃの各出力信号がそれぞれ入力される。位相差検出器５１は各出力信号間の位相差を検出し、振幅比検出器５２は各出力信号間の振幅偏差を検出する。
【００４３】
演算器５３は、１番目のブランチを基準としたときのｊ番目のブランチの相対位相差をθ１ｊ、相対振幅比をＡ１ｊとした場合、以下の（１）〜（３）式に基づいて、校正係数Ｃ１〜Ｃ３を演算する。
【００４４】
【数１】

図３の位相差検出器５１は、図４に詳細構成を示すように、乗算器６１と、低域フィルタ６２と、位相識別器６３とを有する。送信信号とフィードバック信号を乗算器６１で乗算した後、低域フィルタ６２で高周波成分を除去することにより、ｃｏｓθｉｊに比例した偏差成分を得ることができる。
【００４５】
図３の振幅比検出器５２は、図５に詳細構成を示すように、位相補正器６５と、ダイオード６６ａ，６６ｂと、サンプリング器６７ａ，６７ｂと、割り算器６８とを有する。位相補正器６５は、２種類の送信信号のうち一方の送信信号の位相差補正を行って同相入力とする。位相補正器６５の出力と他方の送信信号は、それぞれダイオード６６ａ，６６ｂに入力されて包絡線成分が取り出される。これら包絡線成分はサンプリング器６７ａ，６７ｂでサンプリングされ、サンプリング出力の比が割り算器６８で得られる。
【００４６】
図１の重み係数演算回路２６は、校正係数と周波数変換器２３ａ〜２３ｃの各出力信号に基づいて、所望のアンテナパターンを形成するための送信ウェイトｗ’_Ｔ１〜ｗ’_Ｔ３を演算する。送信ウェイトｗ’_Ｔ１〜ｗ’_Ｔ３は、以下の（４）式で示すように、位相成分ｅ^ｊ ^φ ^ｉと振幅成分Ｍとに分離することができる。
【００４７】
ｗ’Ｔｊ＝Ｍｅ^ｊ ^φ ^ｉ（ｊ＝１，２，３） …（４）
結局、送信系のみの位相変動θ’ｉｊは、θ’ｉｊ＝θｉｊ−φｉ−φｉｊ、振幅変動Ａ’ｉｊは、Ａ’ｉｊ＝Ａｉｊ／（Ｍ・Ｂｉｊ）で求められるので、補償すべき送信系の校正係数Ｃ_Ｔは、（５）〜（７）式のようになる。
【数２】

（５）〜（７）式により、乗算器３３ａ〜３３ｃで重み付けされる校正値を含んだ送信信号に対する重み係数は、（８）式のようになる。
【００４８】
ｗ_Ｔｉ＝ｗ’_Ｔｉ・Ｃ_Ｔｉ（ｉ＝１，２，３） …（８）
上述した（５）〜（８）式で示すような重み付けを行うことにより、アンテナ端から送信される地点で、所望のビームパターンを形成する信号が得られる。
【００４９】
同様に、受信系の校正係数Ｃ_Ｒｉは、以下の（９）〜（１１）式で表される。
【００５０】
【数３】

図１の校正係数演算回路２５は、上述した（５）〜（７）式に基づいて送信系の校正係数を演算するとともに、上述した（９）〜（１１）式に基づいて受信系の校正係数を演算する。また、重み係数演算回路２６は、上述した（８）式に基づいて送信信号に対する重み係数を演算し、同様にして受信信号に対する重み係数も演算する。
【００５１】
次に、パイロット信号挿入器７で挿入されるパイロット信号について説明する。パイロット信号は、例えば、ＰＮ系列（擬似ランダム雑音系列）等で構成され、その信号列は制御局３−基地局２間で既知とする。また、パイロット信号は、フィードバックされる送信信号に時分割で挿入したり、周波数分割で挿入することが可能であるが、いずれの場合も、等振幅の信号を各ブランチごとに同時に挿入する必要がある。
【００５２】
このように、パイロット信号としてＰＮ系列を同時に挿入した場合、フィードバック信号検出器２４で取り込まれた各ブランチのパイロット信号は、相関処理を行うことにより、図６に示すように、その到達タイミングと相関強度を表すインパルス性の強い相関出力になる。この相関出力により、受信系における各ブランチ間の到達遅延時間差ｔ１，ｔ２を観測でき，変動位相差φｉｊを求めることができる。また，ピーク値を比較することにより，受信系の各ブランチ間の相対振幅比Ｂｉｊを検出することができる。
【００５３】
上述した実施形態では，ＰＮ系列のパイロット信号を用いたが，正弦波の搬送波だけをパイロット信号としてフィードバックしてもよい。この場合、制御局３のフィードバック信号検出器２４は，前述の位相差検出器の構成と同様に、乗積器と低域フィルタにより、相対位相差φｉと相対強度比Ｂｉを推定することができる。
【００５４】
このように、第１の実施形態では、基地局２から制御局３に対して、送信信号のフィードバック信号と、アレーアンテナ１での受信信号と、パイロット信号とを多重化して伝送するため、パイロット信号に基づいて、制御局３内で送信信号の相対位相差と相対振幅変動量を検出することができる。また、パイロット信号を用いることにより、周波数シンセサイザ１７，３７から出力される各局部発振信号の同期確立や、基地局２と制御局３との間で伝送される各ブランチ信号の同期確立が可能になる。
【００５５】
また、第１の実施形態では、図４や図５に示すような簡易な構成の位相差検出器５１や振幅比検出器５２を用いて相対位相差と相対振幅変動量を検出できるため、システムの構成を簡略化でき、コストもそれほどかからない。また、アダプティブアンテナにおける送信ビーム制御を精度よく行えるため、高利得かつ狭ビームにより端末局を追尾することができ、一つの基地局２当たりのカバーエリアを拡大でき、ハンドオフ先基地局２の回線混雑による呼損率を低く抑えることもできる。
【００５６】
さらに、メインビームに比べて角度的にセンシティブなヌルの制御を精度よく行えるため、隣接基地局２や他の基地局２と通信中の端末局への干渉を抑えることができ、通信品質を改善できるとともに、システム全体としてのユーザ収容能力の向上が図れる。
【００５７】
なお、上述した実施形態では、図２に示すように、送信信号とパイロット信号を周波数多重する方式について説明したが、送信信号とパイロット信号を時分割多重して制御局３にフィードバックする方式を採用してもよい。
【００５８】
この方式を採用すれば、周波数変換器の通過帯域幅を狭くすることができ、また、各コンポーネントのわずかな周波数特性の影響による推定誤差の発生を防止できる。
【００５９】
また、光ファイバ中では、多重されている受信信号、送信信号およびパイロット信号を受信後に分離することは容易なため、通信中でも校正を行うことができ、校正のために通信が遮断されるような不具合が起きなくなる。
【００６０】
（第２の実施形態）
第２の実施形態は、送信信号の絶対位相を検出するものである。
【００６１】
図７は本発明に係る無線通信システムの第２の実施形態のブロック図である。図７では、図１と共通する構成部分には同一符号を付しており、以下では相違点を中心に説明する。
【００６２】
図７の基地局２は、図１の基地局２と同様に構成されている。図７の制御局３は、図１の構成に加えて、重み付けされた送信信号のいずれか一つを選択する切替器（制御局内切替手段）７１を有する。図７の校正係数演算回路２５は、切替器７１で選択された送信信号と、フィードバック信号検出器２４の出力とに基づいて、送信信号の絶対位相と振幅変動の絶対値を検出する。
【００６３】
図７の校正係数演算回路２５の出力Ｃ_Ｔは（１２）式のようになる。
【００６４】
【数４】

ここで、θｉはｉ番目のブランチの絶対位相、Ａｉはｉ番目のブランチの絶対振幅変動量、φｉはパイロット信号を基準として求められたｉ番目の受信ブランチの絶対位相、Ｂｉはパイロット信号を基準として求められたｉ番目の受信ブランチの絶対振幅変動量である。
【００６５】
（１２）式に示すように、θｉとφｉとの差分を演算することにより、送信信号の絶対位相と絶対振幅変動量を演算することができる。
【００６６】
図７の重み係数演算回路２６は、以下の（１３）式に基づいて送信信号の重み係数ｗ_Ｔｉを演算する。
【００６７】
ｗ_Ｔｉ＝ｗ’_Ｔｉ・Ｃ_Ｔｉ（ｉ＝１，２，３） …（１３）
アダプティブアンテナを有する無線通信システムでは、送信信号の相対位相と相対振幅変動量がわかれば、正しい送信信号を形成できるが、それ以外の目的で各送信ブランチの絶対位相と絶対振幅変動値を知る必要がある場合に、上述した第２の実施形態は有効である。
【００６８】
また、第２の実施形態は、送信信号がフィードバック伝送経路を介して戻ってくるまでの遅延時間、すなわち位相回転が信号の１シンボル長に比べて十分短い場合に有効である。
【００６９】
（第３の実施形態）
第３の実施形態は、パイロット信号なしで絶対位相差と絶対振幅変動量を検出するものである。
【００７０】
図８は本発明に係る無線通信システムの第３の実施形態のブロック図である。図８では、図７と共通する構成部分には同一符号を付しており、以下では相違点を中心に説明する。
【００７１】
図８の無線通信システムは、パイロット信号を伝送しない代わりに、制御局３から基地局２に伝送された送信信号を制御局３にフィードバックする校正用の伝送経路を有することを特徴とする。
【００７２】
図８の基地局２は、制御局３からの送信信号のいずれか一つを選択する切替器（基地局内切替手段）７２と、切替器７２で選択された信号を増幅する増幅器７３と、増幅器７３で増幅された信号の周波数を変換する周波数変換器（第２の周波数変換手段）７４と、周波数変換器７４の出力信号を光信号に変換する光／電気変換器（第２の電気／光変換手段）７５とを有する。
【００７３】
また、図８の制御局３は、基地局２から伝送されてきた送信信号のフィードバック信号を電気信号に変換する光／電気変換器（第２の光／電気変換手段）７６を有する。光／電気変換器７６の出力信号は、フィードバック信号検出器２４に入力される。
【００７４】
図８の無線通信システムでは、基地局２内の切替器７２と制御局３内の切替器７１を順次切り替えて、送信ブランチを一つずつ校正する。ただし、現在校正しているアンテナ素子に対応するブランチを、制御局３と基地局２はともに把握しているものとする。
【００７５】
また、図８の無線通信システムでは、各送信ブランチの位相差と振幅変動量は互いに異なっているが、専用のフィードバック伝送経路の位相差と振幅変動量は常に共通であるため、校正係数演算回路２５で求められた各ブランチの校正係数は、ブランチ間で相対的な値として求められる。図８に示すようなアダプティブアンテナを有するシステムでは、相対位相と相対振幅が一定であればアンテナパターンは一意に定まるため、絶対的な位相や振幅変動量がわからなくても、校正を正しく行うことができる。
【００７６】
また、図８の無線通信システムにおける受信系の校正は、第１の実施形態と同様に、送信系の校正が確立した後、基地局２において送信信号を受信系を介して制御局３にフィードバックし、制御局３で送信信号に対する重み係数で重み付けした送信信号と比較することにより、受信系の校正係数を求めることができる。
【００７７】
このように、第３の実施形態では、パイロット信号を用いることなく相対位相差と相対振幅変動量を検出できるため、基地局２内でパイロット信号を挿入して多重化する処理が不要となり、また、制御局３内でパイロット信号を分離抽出する処理も不要となる。したがって、システムの構成を簡略化することができる。
【００７８】
（第４の実施形態）
上述した第１〜第３の実施形態では、重み係数演算回路２６にて、校正係数を加味した送信信号に対する重み係数を生成して送信信号の重み付けを行う例を説明したが、送信ウェイトによる送信信号の重み付けとは別個に、校正係数による送信信号の重み付けを行ってもよい。
【００７９】
図９は本発明に係る無線通信システムの第４の実施形態のブロック図である。図９では図７と共通する構成部分には同一符号を付しており、以下では相違点を中心に説明する。
【００８０】
図９の基地局２は、図７と同様に構成されている。また、図９の制御局３内の校正係数演算回路２５は、図７と同様の処理を行うが、その処理結果は、重み係数演算回路２６ではなく、送信系に新たに設けられた乗算器（第３の重み付け手段）７７ａ〜７７ｃに供給される。
【００８１】
また、重み係数演算回路２６は、校正係数演算回路２５で演算された校正係数を考慮に入れずに、送信ウェイトと受信ウェイトを演算する。乗算器３３ａ〜３３ｃは、送信ウェイトに基づいて送信信号の重み付けを行う。また、新たに追加された乗算器７７ａ〜７７ｃは、重み付けされた送信信号に対して、校正係数に基づいてさらに重み付けを行う。
【００８２】
なお、上述した図８の無線通信システムについても、図９と同様に、送信ウェイトによる重み付けと校正係数による重み付けとを別々に行ってもよい。
【００８３】
図１０は図８を変形した無線通信システムのブロック図である。図１０の基地局２は、図８と同様に構成されている。また、図１０の制御局３内の重み係数演算回路２６は、校正係数演算回路２５で演算された校正係数を考慮に入れずに、送信ウェイトと受信ウェイトを演算する。乗算器３３ａ〜３３ｃは、送信ウェイトに基づいて送信信号の重み付けを行う。また、新たに追加された乗算器７７ａ〜７７ｃは、重み付けされた送信信号に対して、校正係数に基づいてさらに重み付けを行う。
【００８４】
このように、第４の実施形態では、送信ウェイトによる重み付けと、校正係数による重み付けとを別々に行うため、どちらか一方のみを行うようにすることも可能になる。
【００８５】
（その他の実施形態）
上述した各実施形態では、ＲＯＦ内の伝送方式として副搬送波多重（ＳＣＭ）方式を用いる例を説明したが、ＳＣＭ以外の伝送方式、例えば、波長多重伝送方式、複数の光ファイバをそれぞれ別々のブランチに割り当てる方式、時分割多重伝送方式、符号分割多重方式による方法等でも同様のシステムを構築できる。
【００８６】
また、上述した各実施形態において、送信用の光ファイバケーブルと受信用の光ファイバケーブルとを別個に設けてもよいが、送受信信号は時分割複信または周波数分割複信されるので、１本の光ファイバで送受信を行ってもよい。
【００８７】
さらに、上述した実施形態では、基地局２と制御局３を接続する有線通信媒体として光ファイバを用いる例を説明したが、同軸ケーブルやイーサネットケーブル等を用いたシステムでも、同様の校正処理を行うことができ、同様の効果が得られる。
【００８８】
【発明の効果】
以上詳細に説明したように、本発明によれば、制御局から基地局に伝送された送信信号を制御局にフィードバックさせ、送信信号とフィードバックされた信号との比較結果、またはフィードバックされた信号のいずれか２つの信号の比較結果に基づいて、送信信号の位相および振幅調整を行うため、制御局および基地局内を送信信号が伝搬する間に生じた位相差や振幅変動量を簡易かつ精度よく校正することができる。
【００８９】
また、本発明によれば、通信中においても校正処理を行えるため、校正のために通信が遮断されるおそれもない。
【図面の簡単な説明】
【図１】本発明に係る無線通信システムの第１の実施形態のブロック図。
【図２】合成器で周波数多重化された信号の周波数スペクトル図。
【図３】校正係数演算回路の詳細構成を示すブロック図。
【図４】位相差検出器の詳細構成を示すブロック図。
【図５】振幅比検出器の詳細構成を示すブロック図。
【図６】パイロット信号の到達タイミングと相関強度を示す図。
【図７】本発明に係る無線通信システムの第２の実施形態のブロック図。
【図８】本発明に係る無線通信システムの第３の実施形態のブロック図。
【図９】本発明に係る無線通信システムの第４の実施形態のブロック図。
【図１０】第４の実施形態の変形例を示すブロック図。
【符号の説明】
１アレーアンテナ
１ａ〜１ｃアンテナ素子
２基地局
３制御局
４光ファイバ
５ａ〜５ｃサーキュレータ
６ａ〜６ｃ，１０ａ〜１０ｃ，２８，３５合成器
７パイロット信号挿入器
８ａ〜８ｃローノイズアンプ
９ａ〜９ｃ，１４ａ〜１４ｃ，２３ａ〜２３ｃ，３４ａ〜３４ｃ周波数変換器
１１，３６ａ〜３６ｃ電気／光変換器
１２，２１光／電気変換器
１３，２２，３２ａ〜３２ｃ分配器
１５増幅器
１６ａ〜１６ｃカップラ
１７周波数シンセサイザ
２４フィードバック信号検出器
２５校正係数演算回路
２６重み係数演算回路
２７ａ〜２７ｃ，３３ａ〜３３ｃ乗算器
２９復調器
３１変調器[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention performs data communication between a wireless base station having an array antenna for performing wireless communication with a mobile object and a control station that controls the wireless base station via a wired communication medium such as an optical fiber. The present invention relates to a wireless communication system.
[0002]
[Prior art]
ROF (Radio On Fiber) that connects a plurality of wireless base stations having a relatively small coverage area and one centralized control station with an optical fiber, converts wireless signals into optical signals between each base station and the control station, and transmits the optical signals. The system is excellent in reliability and broadband, and can provide a precise service. Therefore, the system is used as an infrastructure for FTTH (Fiber To The Home), subscriber radio, and ITS (Intelligent Transport System). It is valid.
[0003]
In particular, when constructing an ROF system, if a control station is provided with a modem and a control device and each base station has the minimum necessary device configuration, the base station can be simplified, downsized, and reduced in cost. become. For this reason, many base stations can be arranged along roads, underground shopping malls, tunnels, and the like, and efficient and economic infrastructure construction can be achieved.
[0004]
On the other hand, as an antenna of a base station, an adaptive antenna technology for forming a cover area of an arbitrary shape by giving directivity to a desired terminal station or suppressing interference from other stations has attracted attention. ing.
[0005]
The adaptive antenna technology controls a radiation pattern by weighting signals transmitted and received from a plurality of antenna elements with respect to phase and amplitude. As a method of controlling the radiation pattern, there are mainly a method of performing weighting using an analog element such as an amplifier and a phase shifter, and a method of performing complex weighting by digital signal processing after conversion into a digital signal.
[0006]
Several wireless communication systems have been reported in which this adaptive antenna is provided in a base station and connected to a control station using the ROF technique (for example, JP-A-5-102894 and JP-A-10-145286). In a wireless communication system having an adaptive antenna, a technique for transmitting a wireless signal different for each antenna element while maintaining a relative phase difference and a relative intensity difference between a base station and a control station is required.
[0007]
For this reason, in a conventional report, as a transmission mode of ROF, wavelength multiplex transmission in which signal processing other than frequency conversion is not performed on a radio signal, or a method of allocating an optical fiber to each branch is adopted. Hereinafter, a system that processes signals transmitted and received from one antenna element is referred to as a branch.
[0008]
In the method of providing an optical fiber for each branch, the number of optical fibers connecting the base station and the control station is greatly increased, so that the use efficiency of the optical fiber is reduced and the control station connected to a plurality of base stations is controlled. The configuration of the optical transmission system on the side becomes complicated and the scale becomes large. That is, the ROF technique for a wireless communication system having an adaptive antenna has a problem that the components of the optical transmission system become complicated and large-scale, and it is difficult to simplify and reduce the configurations of the base station and the control station.
[0009]
On the other hand, in a transmission system using an optical fiber, a subcarrier multiplex transmission (SCM) is known as a method of multiplexing a plurality of wireless signals on a frequency axis by one light source. When SCM is used as a method of realizing ROF, only one optical fiber is required for transmission and reception, so that system construction can be reduced in cost, and an optical multiplexer / demultiplexer is not required and a light source can be used. There are merits such as saving. Therefore, it is effective to temporarily convert the transmission / reception signals of each branch, assign a subcarrier to each, and transmit the signals in the optical fiber.
[0010]
[Problems to be solved by the invention]
However, in the above two methods, since a pair of an E / O converter (electrical / optical converter) and an O / E converter (optical / electrical converter) is assigned to each antenna element, the base station and the control station are allocated to each antenna element. Requires as many pairs as branches. That is, there is a problem that the components of the optical transmission unit of the base station and the control station are greatly increased, and the configuration is complicated and large.
[0011]
In addition, when performing wavelength division multiplexing transmission between a base station and a control station, it is necessary to add a configuration such as an optical multiplexer, an optical demultiplexer, and a wavelength controller of a light source, which results in a very expensive system. Would.
[0012]
Further, in the method using the SCM, there is a problem that a multiplexed signal of each branch cannot be correctly extracted unless carrier synchronization and timing synchronization are obtained between the base station and the control station.
[0013]
The present invention has been made in view of such a point, and an object of the present invention is to simply and accurately adjust the phase and amplitude of a transmission signal transmitted from a control station to a base station without complicating the configuration. An object of the present invention is to provide a wireless communication system that can perform the communication.
[0014]
[Means for Solving the Problems]
In order to solve the above-described problem, the invention according to claim 1 includes a wireless communication terminal, a base station that performs wireless communication with the wireless communication terminal, and a control station that is connected to the base station via a wired transmission path. In the wireless communication system consisting of, the base station, an array antenna consisting of a plurality of antenna elements, each transmission signal corresponding to each antenna element transmitted from the control station via the wired transmission path, The control station has feedback means for feeding back to the control station via the wired transmission path, and the control station compares at least two signals from among the transmission signals fed back from the feedback means, and calculates a phase difference and A plurality of antenna elements based on the phase difference and / or the amount of amplitude fluctuation detected by the comparison / detection means. And a compensating means for compensating the transmission signal of each corresponding to.
According to the first aspect of the present invention, the control signal is compared with the transmission signal transmitted to the base station and the feedback signal to detect the phase difference and the amplitude fluctuation amount. It can be carried out.
[0015]
According to the second and third aspects of the present invention, when the transmission signal is fed back to the control station, a pilot signal is inserted into the feedback signal. Therefore, the relative phase difference and the relative amplitude variation in the receiving system are detected by the feedback signal. According to the detection result, the relative phase difference and the relative amplitude fluctuation amount of the transmission system can be detected.
[0016]
According to the fourth aspect of the present invention, the absolute phase difference and the absolute amplitude variation of each transmission signal can be detected.
[0017]
According to the fifth aspect of the present invention, since any one of the transmission signals corresponding to each antenna element can be arbitrarily selected, the absolute phase difference and the absolute amplitude variation of each transmission signal can be detected.
[0018]
In the inventions of claims 5 to 7, since a dedicated transmission medium for feeding back a transmission signal to a control station is provided, the relative phase difference and the relative amplitude fluctuation amount can be detected without a pilot signal.
[0019]
According to the eighth aspect of the present invention, the weighting factor is calculated in consideration of the calibration factor for compensating the phase difference and the amplitude variation, so that the weighting and calibration of the transmission signal can be performed collectively.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a wireless communication system to which the present invention is applied will be specifically described with reference to the drawings.
[0021]
(1st Embodiment)
FIG. 1 is a block diagram of a first embodiment of a wireless communication system according to the present invention. The system shown in FIG. 1 shows an example in which a base station 2 having an adaptive antenna 1 and a control station 3 are connected by an optical fiber 4 to perform subcarrier multiplex transmission. Although the adaptive antenna 1 of FIG. 1 has three antenna elements 1a to 1c, the number of the antenna elements 1a to 1c is not particularly limited.
[0022]
1 includes circulators 5a to 5c for switching between transmission and reception, combiners (synthesis means) 6a to 6c for combining transmission and reception signals, and a transmission signal to be fed back to the control station 3 as a configuration of a reception system. A pilot signal inserter (pilot signal inserting means) 7 that inserts a pilot signal into low frequency amplifiers 8a to 8c that amplify the output signal of pilot signal inserter 7, and output signals of low noise amplifiers 8a to 8c at different frequencies Frequency converters (first frequency conversion means) 9a to 9c for down-converting the signals, and synthesizers (frequency multiplexing means) 10a to 10c for multiplexing each frequency signal output from the frequency converters 9a to 9c. , Which converts the signal synthesized by the synthesizers 10a to 10c into an optical signal and transmits the optical signal to the control station 3 via the optical fiber 4. And a converter (first electric / optical conversion means) 11.
[0023]
The base station 2 in FIG. 1 includes, as a transmission system configuration, an optical / electrical converter 12 that converts an optical signal transmitted from the control station 3 into an electric signal, and an output signal of the optical / electrical converter 12. A distributor 13 that distributes a plurality of frequency signals, frequency converters 14a to 14c that convert the frequency signals distributed by the distributor 13 into radio frequency signals, and amplifies output signals of the frequency converters 14a to 14c. It has amplifiers 15a to 15c and couplers 16a to 16c for branching output signals of the amplifiers 15a to 15c to circulators 5a to 5c and combiners 6a to 6c.
[0024]
In addition, the base station 2 of FIG. 1 has a frequency synthesizer 17 that supplies a local oscillation signal to each of the frequency converters 9a to 9c and 14a to 14c. The frequency synthesizer 17 has a plurality of local oscillators each outputting a signal having a different frequency, or a single local oscillator and a plurality of frequency signals obtained by multiplying or dividing a local oscillation signal output from the local oscillator. And a frequency divider that outputs
[0025]
On the other hand, the control station 3 shown in FIG. 1 includes, as a configuration of a receiving system, an optical / electrical converter (optical / electrical conversion means) 21 for converting an optical signal transmitted from the base station 2 into an electric signal, and an optical / electrical A distributor (distribution unit) 22 that distributes the output signal of the converter 21 into a plurality of signals; and a frequency converter (third frequency conversion unit) that converts each signal output from the distributor 22 into a signal having a different frequency. ) 23a to 23c, a feedback signal detector (feedback means) 24 for detecting a feedback signal of a transmission signal based on output signals of the frequency converters 23a to 23c, and a calibration coefficient calculation for calculating a calibration coefficient based on the feedback signal A circuit (comparison means) 25, an adaptive antenna weight coefficient calculation circuit (weight coefficient calculation means) 26 for calculating a transmission / reception weight coefficient based on the calibration coefficient, Multipliers (first weighting means) 27a to 27c for weighting the received signal based on the calculated weighting coefficients, a combiner 28 for combining the output signals of the multipliers 27a to 27c, and a combiner 28 And a demodulator 29 for demodulating the converted signal.
[0026]
Further, the control station 3 of FIG. 1 includes, as a transmission system configuration, a modulator 31 that generates a modulation signal for transmission, distributors 32a to 32c that distributes the modulation signal into a plurality, and weights the distributed modulation signal. Multipliers (second weighting means) 33a to 33c for weighting based on the coefficients; frequency converters 34a to 34c for converting the output signals of the multipliers 33a to 33c into signals of different frequencies; and frequency converters 34a to 34c. A combiner 35 for multiplexing the output signal of 34 c and an electric / optical converter 36 for converting the signal multiplexed by the combiner 35 into an optical signal and transmitting the optical signal to the base station 2 via the optical fiber 4. .
[0027]
In addition, the control station 3 of FIG. 1 has a frequency synthesizer 37 that supplies a local oscillation signal to each of the frequency converters 23a to 23c and 34a to 34c. The frequency synthesizer 37 includes a plurality of local oscillators each outputting a signal having a different frequency, or a single local oscillator and a plurality of frequency signals obtained by multiplying or dividing the local oscillation signal output from the local oscillator. And a frequency divider that outputs In the present embodiment, it is assumed that the frequency synthesizer 17 in the base station 2 and the frequency synthesizer 37 in the control station 3 are synchronized in frequency and timing.
[0028]
In the base station 2 of FIG. 1, the combiners 6a to 6c, the pilot signal inserter 7, the low noise amplifiers 8a to 8c, the frequency converters 9a to 9c, the combiner 9, and the electric / optical converter 11 correspond to the feedback means. The frequency converters 8a to 8c, 9a to 9c, the synthesizer 10, and the electric / optical converter 11 correspond to a transmission unit. In the control station 2 of FIG. 1, the weight coefficient calculation circuit 26 and the multipliers 27a to 27c and 33a to 33c correspond to compensation means, and the feedback signal detector 24 corresponds to first and second detection means. .
[0029]
The base station 2 in FIG. 1 feeds back a transmission signal transmitted from the control station 3 to the base station 2 to the control station 3 via a receiving system in the base station 2 before radiating the transmission signal from the array antenna 1. Further, the control station 3 compares two of the feedback signals and generates a calibration coefficient for compensating the relative phase difference and the relative amplitude variation of the transmission signal.
[0030]
Hereinafter, the operation of the wireless communication system of FIG. 1 will be described. The signals received by the antenna elements 1a to 1c and the transmission signal transmitted from the control station 3 to the base station 2 are combined by combiners 6a to 6c, and then a pilot signal is inserted by a pilot signal inserter 7. You. Thereafter, the signals are input to the frequency converters 9a to 9c via the low-noise amplifiers 8a to 8c, and are converted into different frequencies for the respective branches corresponding to the antenna elements 1a to 1c. At this time, it is desirable to convert to an intermediate frequency according to the frequency characteristics of the optical fiber 4 and the light source. By converting to the intermediate frequency, the configuration of the optical transmission system can be simplified. The output signals of the frequency converters 9a to 9c are frequency-multiplexed by the combiner 10, converted into optical signals by the electrical / optical converter 11, and transmitted to the base station 2.
[0031]
FIG. 2 is a frequency spectrum diagram of the signal frequency-multiplexed by the synthesizer 10. As shown in FIG. 2, a reception signal at the array antenna 1, a pilot signal, and a transmission signal from the control station 3 are respectively arranged at different frequency intervals, and these are grouped as subcarriers f1 to f3. . Note that a band filter (not shown) provided inside the frequency converters 9a to 9c needs to have a band that can pass a signal group of each subcarrier.
[0032]
The optical signal transmitted to the control station 3 is converted into an electric signal again by the electric / optical converter 21 in the control station 3, and then is divided into a plurality of branch signals by the distributor 22. After these branch signals are converted into the same frequency signal by the frequency converters 23a to 23c, they are input to the feedback signal detector 24 and the multipliers 27a to 27c.
[0033]
The feedback signal detector 24 extracts a transmission signal transmitted by the control station 3, a pilot signal, and a reception signal received by the adaptive antenna 1 from the output signals of the frequency converters 23a to 23c.
[0034]
The calibration coefficient calculation circuit 25 uses the transmission signal of any one of the transmission signals of each branch extracted by the feedback signal detector 24 as a reference to determine the relative phase difference and relative amplitude with the transmission signals of the remaining branches. The deviation is detected, and a calibration coefficient according to the detection result is calculated.
[0035]
The weight coefficient calculating circuit 26 is configured to transmit a transmission signal based on the output signals of the frequency converters 23a to 23c, the calibration coefficient calculated by the calibration coefficient calculating circuit 25, and the transmission / reception weight calculated for beam control. And a weight coefficient for the received signal are calculated.
[0036]
The multipliers 27a to 27c multiply the output signals of the frequency converters 23a to 23c by the weight coefficients calculated by the weight coefficient calculation circuit 26 to weight the received signals. The weighted received signal is input to the demodulator 29 and demodulated.
[0037]
On the other hand, the transmission signal modulated by the modulator 31 in the control station 3 is weighted by the multipliers 33a to 33c by being multiplied by the weight coefficient calculated by the weight coefficient calculation circuit 26. The weighted transmission signals are converted into signals of different frequencies by frequency converters 34a to 34c, and then frequency multiplexed by combiner 35.
[0038]
The frequency-multiplexed transmission signal is converted into an optical signal by an electrical / optical converter 36 and transmitted to the base station 2 via the optical fiber 4.
[0039]
The optical signal transmitted to the base station 2 is split into a plurality of branch signals by a splitter 13, and each branch signal is input to the frequency converters 14a to 14c and up-converted into a radio frequency signal.
[0040]
The output signals of the frequency converters 14a to 14c are input to the amplifiers 15a to 15c and amplified, and then input to the antenna elements 1a to 1c via the couplers 16a to 16c and the circulators 5a to 5c.
[0041]
Next, the detailed configuration and operation of the feedback signal detector 24, the calibration coefficient operation circuit 25, and the weight coefficient operation circuit 26 of FIG. 1 will be described.
[0042]
The calibration coefficient calculation circuit 25 includes a phase difference detector 51, an amplitude ratio detector 52, and a calculator 53, as shown in detail in FIG. The output signals of the frequency converters 23a to 23c are input to both the phase difference detector 51 and the amplitude ratio detector 52, respectively. The phase difference detector 51 detects a phase difference between each output signal, and the amplitude ratio detector 52 detects an amplitude deviation between each output signal.
[0043]
When the relative phase difference of the j-th branch with respect to the first branch is θ1j and the relative amplitude ratio is A1j with reference to the first branch, the arithmetic unit 53 performs calibration based on the following equations (1) to (3). The coefficients C1 to C3 are calculated.
[0044]
(Equation 1)

The phase difference detector 51 in FIG. 3 includes a multiplier 61, a low-pass filter 62, and a phase discriminator 63, as shown in FIG. After multiplying the transmission signal and the feedback signal by the multiplier 61 and removing the high-frequency component by the low-pass filter 62, a deviation component proportional to cos θij can be obtained.
[0045]
The amplitude ratio detector 52 in FIG. 3 includes a phase corrector 65,

diodes

66a and 66b, samplers 67a and 67b, and a divider 68, as shown in FIG. The phase corrector 65 corrects the phase difference of one of the two types of transmission signals to obtain an in-phase input. The output of the phase corrector 65 and the other transmission signal are input to

diodes

66a and 66b, respectively, to extract an envelope component. These envelope components are sampled by the samplers 67a and 67b, and the ratio of the sampling output is obtained by the divider 68.
[0046]
The weighting coefficient calculation circuit 26 in FIG. 1 is configured to transmit a weight w ′ for forming a desired antenna pattern based on the calibration coefficient and each output signal of the frequency converters 23a to 23c._T1~ W '_T3Is calculated. Transmission weight w '_T1~ W '_T3Is the phase component e as shown in the following equation (4).^j ^φ ⁱAnd the amplitude component M.
[0047]
w'Tj = Me^j ^φ ⁱ (J = 1, 2, 3) ... (4)
As a result, the phase variation θ′ij of only the transmission system is determined by θ′ij = θij−φi−φij, and the amplitude variation A′ij is determined by A′ij = Aij / (M · Bij). System calibration coefficient C_TIs as shown in equations (5) to (7).
(Equation 2)

According to the equations (5) to (7), the weight coefficient for the transmission signal including the calibration value weighted by the multipliers 33a to 33c is as shown in the equation (8).
[0048]
w_Ti= W '_Ti・ C_Ti (I = 1, 2, 3) (8)
By performing weighting as shown in the above equations (5) to (8), a signal forming a desired beam pattern can be obtained at a point transmitted from the antenna end.
[0049]
Similarly, the calibration coefficient C of the receiving system_RiIs represented by the following equations (9) to (11).
[0050]
(Equation 3)

The calibration coefficient calculation circuit 25 of FIG. 1 calculates the calibration coefficients of the transmission system based on the above-described equations (5) to (7), and also performs the calibration of the reception system based on the above-described equations (9) to (11). Calculate coefficients. Further, the weight coefficient calculation circuit 26 calculates a weight coefficient for the transmission signal based on the above equation (8), and similarly calculates a weight coefficient for the reception signal.
[0051]
Next, the pilot signal inserted by pilot signal inserter 7 will be described. The pilot signal is composed of, for example, a PN sequence (pseudo-random noise sequence), and its signal sequence is known between the control station 3 and the base station 2. Further, the pilot signal can be inserted into the transmission signal to be fed back in a time-division manner or in a frequency-division manner. In any case, it is necessary to simultaneously insert a signal of equal amplitude for each branch. is there.
[0052]
As described above, when a PN sequence is simultaneously inserted as a pilot signal, the pilot signal of each branch taken in by the feedback signal detector 24 is subjected to a correlation process, as shown in FIG. The correlation output becomes a strong impulse characteristic indicating the intensity. With this correlation output, the arrival delay time differences t1 and t2 between the branches in the receiving system can be observed, and the fluctuation phase difference φij can be obtained. Further, by comparing the peak values, the relative amplitude ratio Bij between the branches of the receiving system can be detected.
[0053]
In the above-described embodiment, a PN sequence pilot signal is used, but only a sine wave carrier may be fed back as a pilot signal. In this case, the feedback signal detector 24 of the control station 3 can estimate the relative phase difference φi and the relative intensity ratio Bi by using a multiplier and a low-pass filter as in the configuration of the phase difference detector described above. .
[0054]
As described above, in the first embodiment, since the base station 2 multiplexes and transmits the feedback signal of the transmission signal, the signal received by the array antenna 1, and the pilot signal to the control station 3, Based on the signal, the control station 3 can detect the relative phase difference and the relative amplitude variation of the transmission signal. Further, by using the pilot signal, it is possible to establish the synchronization of each local oscillation signal output from the

frequency synthesizers

17 and 37 and the synchronization of each branch signal transmitted between the base station 2 and the control station 3. Become.
[0055]
Further, in the first embodiment, since the relative phase difference and the relative amplitude fluctuation amount can be detected using the phase difference detector 51 and the amplitude ratio detector 52 having a simple configuration as shown in FIGS. Can be simplified and the cost is not so high. In addition, since the transmission beam control in the adaptive antenna can be performed with high accuracy, the terminal station can be tracked with a high gain and a narrow beam, the coverage area per one base station 2 can be expanded, and the line congestion of the handoff destination base station 2 can be achieved. Can also reduce the call loss rate.
[0056]
Furthermore, since the null sensitive control that is angularly more sensitive than the main beam can be performed with high precision, interference with a terminal station that is communicating with the adjacent base station 2 or another base station 2 can be suppressed, and communication quality can be improved. In addition to this, it is possible to improve the user accommodation capacity of the entire system.
[0057]
In the above-described embodiment, as shown in FIG. 2, a method of frequency-multiplexing a transmission signal and a pilot signal has been described. However, a method of time-division-multiplexing the transmission signal and the pilot signal and feeding back to the control station 3 is adopted. May be.
[0058]
If this method is adopted, the pass band width of the frequency converter can be narrowed, and the occurrence of an estimation error due to the slight influence of the frequency characteristics of each component can be prevented.
[0059]
Further, in an optical fiber, since it is easy to separate a multiplexed reception signal, transmission signal, and pilot signal after reception, calibration can be performed even during communication, and communication is interrupted for calibration. No problems occur.
[0060]
(Second embodiment)
In the second embodiment, the absolute phase of a transmission signal is detected.
[0061]
FIG. 7 is a block diagram of a second embodiment of the wireless communication system according to the present invention. 7, the same components as those in FIG. 1 are denoted by the same reference numerals, and different points will be mainly described below.
[0062]
The base station 2 in FIG. 7 is configured similarly to the base station 2 in FIG. The control station 3 in FIG. 7 includes a switch (intra-control-station switching unit) 71 that selects any one of the weighted transmission signals in addition to the configuration in FIG. The calibration coefficient calculation circuit 25 in FIG. 7 detects the absolute phase and the absolute value of the amplitude fluctuation of the transmission signal based on the transmission signal selected by the switch 71 and the output of the feedback signal detector 24.
[0063]
The output C of the calibration coefficient calculation circuit 25 of FIG._TIs as shown in equation (12).
[0064]
(Equation 4)

Here, θi is the absolute phase of the i-th branch, Ai is the absolute amplitude fluctuation amount of the i-th branch, φi is the absolute phase of the i-th receiving branch obtained based on the pilot signal, and Bi is the pilot signal. Is the absolute amplitude fluctuation amount of the i-th reception branch obtained as
[0065]
As shown in the equation (12), by calculating the difference between θi and φi, it is possible to calculate the absolute phase and the absolute amplitude variation of the transmission signal.
[0066]
The weight coefficient calculation circuit 26 in FIG. 7 calculates the weight coefficient w of the transmission signal based on the following equation (13)._TiIs calculated.
[0067]
w_Ti= W '_Ti・ C_Ti (I = 1, 2, 3) (13)
In a wireless communication system having an adaptive antenna, a correct transmission signal can be formed if the relative phase and relative amplitude variation of the transmission signal are known, but it is necessary to know the absolute phase and absolute amplitude variation value of each transmission branch for other purposes. When there is, the second embodiment described above is effective.
[0068]
The second embodiment is effective when the delay time until the transmission signal returns via the feedback transmission path, that is, when the phase rotation is sufficiently shorter than the one symbol length of the signal.
[0069]
(Third embodiment)
In the third embodiment, an absolute phase difference and an absolute amplitude variation are detected without a pilot signal.
[0070]
FIG. 8 is a block diagram of a third embodiment of the wireless communication system according to the present invention. In FIG. 8, components common to those in FIG. 7 are denoted by the same reference numerals, and the following description will focus on differences.
[0071]
The wireless communication system of FIG. 8 has a transmission path for calibration that feeds back a transmission signal transmitted from the control station 3 to the base station 2 to the control station 3 instead of transmitting no pilot signal.
[0072]
8 includes a switch (intra-base-station switching unit) 72 for selecting any one of the transmission signals from the control station 3, an amplifier 73 for amplifying the signal selected by the switch 72, and an amplifier 73. A frequency converter (second frequency conversion means) 74 for converting the frequency of the signal amplified by 73 and an optical / electrical converter (second electric / optical) for converting an output signal of the frequency converter 74 into an optical signal. (Conversion means) 75.
[0073]
The control station 3 in FIG. 8 includes an optical / electrical converter (second optical / electrical conversion unit) 76 that converts a feedback signal of a transmission signal transmitted from the base station 2 into an electric signal. The output signal of the optical / electrical converter 76 is input to the feedback signal detector 24.
[0074]
In the wireless communication system of FIG. 8, the switch 72 in the base station 2 and the switch 71 in the control station 3 are sequentially switched to calibrate the transmission branches one by one. However, it is assumed that both the control station 3 and the base station 2 grasp the branch corresponding to the antenna element currently being calibrated.
[0075]
Further, in the wireless communication system of FIG. 8, the phase difference and the amplitude variation of each transmission branch are different from each other, but the phase difference and the amplitude variation of the dedicated feedback transmission path are always common, so the calibration coefficient calculation circuit The calibration coefficient of each branch obtained in 25 is obtained as a relative value between branches. In a system having an adaptive antenna as shown in FIG. 8, if the relative phase and the relative amplitude are constant, the antenna pattern is uniquely determined. Therefore, it is necessary to perform calibration correctly even if the absolute phase and amplitude fluctuation are unknown. Can be.
[0076]
Further, in the calibration of the receiving system in the wireless communication system of FIG. 8, as in the first embodiment, after the calibration of the transmitting system is established, the base station 2 feeds back the transmission signal to the control station 3 via the receiving system. Then, by comparing the transmission signal with the transmission signal weighted by the weight coefficient for the transmission signal in the control station 3, the calibration coefficient of the reception system can be obtained.
[0077]
As described above, in the third embodiment, since the relative phase difference and the relative amplitude fluctuation amount can be detected without using the pilot signal, the process of inserting and multiplexing the pilot signal in the base station 2 becomes unnecessary, and In addition, the process of separating and extracting the pilot signal in the control station 3 becomes unnecessary. Therefore, the configuration of the system can be simplified.
[0078]
(Fourth embodiment)
In the above-described first to third embodiments, the example has been described in which the weighting factor calculation circuit 26 generates a weighting factor for the transmission signal in consideration of the calibration coefficient and weights the transmission signal. The transmission signal may be weighted by the calibration coefficient separately from the signal weighting.
[0079]
FIG. 9 is a block diagram of a fourth embodiment of the wireless communication system according to the present invention. In FIG. 9, the same components as those in FIG. 7 are denoted by the same reference numerals, and different points will be mainly described below.
[0080]
The base station 2 of FIG. 9 has the same configuration as that of FIG. Also, the calibration coefficient calculation circuit 25 in the control station 3 in FIG. 9 performs the same processing as in FIG. 7, but the processing result is not a weight coefficient calculation circuit 26 but a multiplier newly provided in the transmission system. (Third weighting means) It is supplied to 77a to 77c.
[0081]
Further, the weight coefficient calculation circuit 26 calculates the transmission weight and the reception weight without considering the calibration coefficient calculated by the calibration coefficient calculation circuit 25. The multipliers 33a to 33c weight transmission signals based on transmission weights. Further, the newly added multipliers 77a to 77c further weight the weighted transmission signals based on the calibration coefficients.
[0082]
In the wireless communication system of FIG. 8 described above, similarly to FIG. 9, weighting by the transmission weight and weighting by the calibration coefficient may be performed separately.
[0083]
FIG. 10 is a block diagram of a wireless communication system obtained by modifying FIG. The base station 2 in FIG. 10 is configured similarly to FIG. Further, the weight coefficient calculation circuit 26 in the control station 3 in FIG. 10 calculates the transmission weight and the reception weight without taking the calibration coefficient calculated by the calibration coefficient calculation circuit 25 into account. The multipliers 33a to 33c weight transmission signals based on transmission weights. Further, the newly added multipliers 77a to 77c further weight the weighted transmission signals based on the calibration coefficients.
[0084]
As described above, in the fourth embodiment, since the weighting by the transmission weight and the weighting by the calibration coefficient are performed separately, it is possible to perform only one of them.
[0085]
(Other embodiments)
In each of the above-described embodiments, an example in which the subcarrier multiplexing (SCM) system is used as the transmission system in the ROF has been described. , A time-division multiplexing transmission method, a code-division multiplexing method, etc., a similar system can be constructed.
[0086]
In each of the above-described embodiments, the transmission optical fiber cable and the reception optical fiber cable may be provided separately. However, since the transmission and reception signals are time-division duplex or frequency-division duplex, one cable is used. The transmission and reception may be performed using the optical fiber.
[0087]
Further, in the above-described embodiment, an example in which an optical fiber is used as a wired communication medium for connecting the base station 2 and the control station 3 has been described. However, a similar calibration process is performed in a system using a coaxial cable, an Ethernet cable, or the like. The same effect can be obtained.
[0088]
【The invention's effect】
As described in detail above, according to the present invention, the transmission signal transmitted from the control station to the base station is fed back to the control station, and the comparison result between the transmission signal and the feedback signal, or the feedback signal To adjust the phase and amplitude of the transmission signal based on the comparison result of any two signals, simply and accurately calibrate the phase difference and amplitude fluctuation amount generated while the transmission signal propagates in the control station and the base station. can do.
[0089]
Further, according to the present invention, since the calibration process can be performed even during communication, there is no possibility that communication will be interrupted for calibration.
[Brief description of the drawings]
FIG. 1 is a block diagram of a first embodiment of a wireless communication system according to the present invention.
FIG. 2 is a frequency spectrum diagram of a signal frequency-multiplexed by a synthesizer.
FIG. 3 is a block diagram showing a detailed configuration of a calibration coefficient calculation circuit.
FIG. 4 is a block diagram showing a detailed configuration of a phase difference detector.
FIG. 5 is a block diagram showing a detailed configuration of an amplitude ratio detector.
FIG. 6 is a diagram showing arrival timing and correlation strength of a pilot signal.
FIG. 7 is a block diagram of a second embodiment of the wireless communication system according to the present invention.
FIG. 8 is a block diagram of a third embodiment of the wireless communication system according to the present invention.
FIG. 9 is a block diagram of a fourth embodiment of the wireless communication system according to the present invention.
FIG. 10 is a block diagram showing a modification of the fourth embodiment.
[Explanation of symbols]
1 Array antenna
1a-1c antenna element
2 base stations
3 Control station
4 Optical fiber
5a-5c circulator
6a to 6c, 10a to 10c, 28, 35 synthesizer
7 Pilot signal inserter
8a-8c low noise amplifier
9a to 9c, 14a to 14c, 23a to 23c, 34a to 34c Frequency converter
11,36a-36c Electric / optical converter
12,21 Optical / electrical converter
13,22,32a-32c Distributor
15 Amplifier
16a-16c coupler
17 Frequency synthesizer
24 Feedback signal detector
25 Calibration coefficient calculation circuit
26 Weight coefficient calculation circuit
27a-27c, 33a-33c Multipliers
29 demodulator
31 modulator

Claims

In a wireless communication system including a wireless communication terminal, a base station performing wireless communication with the wireless communication terminal, and a control station connected to the base station via a wired transmission path,
The base station comprises:
An array antenna comprising a plurality of antenna elements;
Each transmission signal corresponding to each of the antenna elements transmitted from the control station via the wired transmission line, feedback means for feeding back to the control station via the wired transmission line,
The control station,
From among the transmission signals fed back from the feedback means, at least two signals are compared, and a phase difference and / or a comparison detection means for detecting an amplitude fluctuation amount,
A wireless communication system, comprising: a compensator for compensating each transmission signal corresponding to the plurality of antenna elements based on the phase difference and / or the amplitude variation detected by the comparison detector.

The feedback means includes:
Pilot signal insertion means for inserting a pilot signal having a known phase and / or amplitude into each transmission signal to the plurality of antenna elements,
Transmitting means for multiplexing each output signal of the pilot signal inserting means and transmitting the multiplexed signal to the control station via the wired transmission path,
The comparison detection means,
First detection means for detecting a phase difference and / or an amplitude variation of a reception system path from the base station to the control station based on the pilot signal,
And a second detection unit configured to detect a phase difference and / or an amplitude variation of a transmission system path from the control station to the base station based on a detection result of the first detection unit. The wireless communication system according to claim 1.

The feedback means includes:
Combining means for combining each transmission signal to the plurality of antenna elements and a reception signal at the corresponding antenna element,
Pilot signal insertion means for inserting a pilot signal having a known phase and / or amplitude into each signal synthesized by the synthesis means,
A plurality of first frequency conversion means for converting each output signal of the pilot signal insertion means into a signal of a different frequency,
Frequency multiplexing means for multiplexing each output signal of the plurality of first frequency conversion means,
Electrical / optical conversion means for optically modulating the signal multiplexed by the frequency multiplexing means and transmitting the modulated signal to the control station via the wired transmission path,
The control station,
An optical / electrical conversion unit for converting an optical signal transmitted from the electric / optical conversion unit via the wired transmission path into an electric signal;
Distribution means for distributing the electric signal converted by the optical / electrical conversion means into signals of a plurality of different frequencies,
A plurality of second frequency conversion means for converting each signal distributed by the distribution means into a signal of the same frequency,
The comparison detection means,
Extracting means for extracting the pilot signal and a feedback signal of a transmission signal to the plurality of antenna elements from each output signal of the plurality of second frequency conversion means;
First detection means for detecting a phase difference and / or an amplitude variation of a reception system path from the base station to the control station based on the pilot signal,
A second detection unit configured to detect a phase difference and / or an amplitude variation of a transmission path from the control station to the base station based on a detection result of the first detection unit. Item 2. The wireless communication system according to item 1.

In a wireless communication system including a wireless communication terminal, a base station performing wireless communication with the wireless communication terminal, and a control station connected to the base station via a wired transmission path,
The base station comprises:
An array antenna comprising a plurality of antenna elements;
Each transmission signal corresponding to the antenna element transmitted from the control station via the wired transmission line, a feedback unit for feedback to the control station via the wired transmission line,
The control station,
At least one of the transmission signals corresponding to the plurality of antenna elements is compared with at least one of the signals fed back from the feedback unit, and an absolute phase difference between the two and / or an absolute amplitude variation is detected. Comparison detection means;
And a compensating means for compensating each transmission signal corresponding to the plurality of antenna elements based on a comparison result of the comparison detecting means.

The control station,
Having a control station switching means for selecting any one of the transmission signals corresponding to the plurality of antenna elements,
The comparison and detection unit is configured to perform an absolute phase difference and / or an absolute amplitude change of the transmission signal based on the transmission signal selected by the control-station switching unit and a signal fed back from the feedback unit corresponding to the transmission signal. The wireless communication system according to claim 4, wherein the amount is detected.

The feedback means has a dedicated transmission path for selecting any one of the transmission signals corresponding to the plurality of antenna elements and feeding it back to the control station,
The comparing and detecting means compares a signal fed back to the control station via the dedicated transmission path with a transmission signal corresponding to the signal, and detects an absolute phase difference and / or an absolute amplitude variation of the transmission signal. The wireless communication system according to claim 4, wherein the communication is performed.

The feedback means includes:
Combining means for combining each transmission signal corresponding to the plurality of antenna elements and a reception signal at the corresponding antenna element,
A plurality of first frequency conversion means for converting each signal synthesized by the synthesis means into a signal having a different frequency,
Frequency multiplexing means for multiplexing each output signal of the plurality of first frequency conversion means,
First electrical / optical conversion means for optically modulating the signal multiplexed by the frequency multiplexing means and transmitting the modulated signal to the preceding control station via the wired transmission path;
A switching unit in a base station that selects any one of the transmission signals to the plurality of antenna elements,
Second frequency conversion means for frequency-converting the transmission signal selected by the intra-base-station switching means,
Second electrical / optical conversion means for optically modulating an output signal of the second frequency conversion means and transmitting the modulated signal to the control station via the dedicated transmission path,
The control station,
First optical / electrical conversion means for converting an optical signal transmitted from the first electrical / optical conversion means via the wired transmission path into an electric signal;
Distribution means for distributing the electric signal converted by the first optical / electrical conversion means into a plurality of frequency signals;
A plurality of third frequency conversion means for converting each signal distributed by the distribution means into a signal of the same frequency;
Second optical / electrical conversion means for converting an optical signal transmitted from the second electric / optical conversion means via the dedicated transmission line into an electric signal;
Having a control station switching means for selecting any one of the transmission signals corresponding to the plurality of antenna elements,
The comparing and detecting means sequentially switches between the in-base-station switching means and the in-control-station switching means, and for each of the antenna elements, a transmission signal corresponding to the signal and an output of the second optical / electrical conversion means. 5. The wireless communication system according to claim 4, wherein the signal is compared with a signal to detect an absolute phase difference and / or an absolute amplitude variation of the transmission signal.

The array antenna is an adaptive antenna capable of changing the directivity of the transmission and reception beams,
The control station,
An adaptive antenna weighting factor calculation unit that calculates an adaptive antenna weighting factor for a phase and an amplitude for each of the antenna elements to change the directivity of the adaptive antenna, further comprising:
The compensation means,
Based on a comparison result of the comparison detection unit, a calibration coefficient calculation unit that calculates a calibration coefficient for estimating a phase difference and / or an amplitude variation of each transmission signal corresponding to the plurality of antenna elements,
Weight coefficient calculating means for calculating a transmission weight coefficient and a reception weight coefficient based on the adaptive antenna weight coefficient and the calibration coefficient,
First weighting means for weighting a reception signal at the plurality of antenna elements based on the reception weight coefficient;
The wireless communication system according to claim 4, further comprising a second weighting unit that weights the transmission signals to the plurality of antenna elements based on the transmission weight coefficient.

The wireless communication system according to claim 1, wherein the wired transmission path is a transmission path using an optical fiber.